Expériences sensibles de la mobilité urbaine

Cette recherche porte sur l'expérience de la mobilité en transports collectifs urbains et prend son origine au croisement de deux questions complémentaires : qu'est-ce que faire un trajet en ville, quelles modalités de compréhension de l'espace urbain la traversée rend-elle possible ? Questions qui invitent à l'ouverture de trois chantiers, méthodologique, théorique et pratique

Expériences sensibles de la mobilité urbaine

Cette recherche porte sur l'expérience de la mobilité en transports collectifs urbains et prend son origine au croisement de deux questions complémentaires : qu'est-ce que faire un trajet en ville, quelles modalités de compréhension de l'espace urbain la traversée rend-elle possible ? Questions qui invitent à l'ouverture de trois chantiers, méthodologique, théorique et pratique

The jointly scheduling of hard periodic tasks with soft aperiodic events within the Real-Time Specification for Java (RTSJ)

The studied problem is the jointly scheduling of hard periodic tasks with soft aperiodic events, where the response times of soft tasks have to be as low as possible while the warranty to meet their deadlines has to be given to hard tasks. A lot of theoretical solutions have been proposed these past two decades but we are interested on the implementability of these solutions under the real-time specification for Java (RTSJ), without changing the scheduler. This led us to adapt the existing algorithms to operate at a user land level in the system, to propose some optimizations and counter measures in order to balance the lost of performances and finally to set up an approximate slack stealer algorithm specifically designed to take into account RTSJ restrictions. We propose new classes to extend the RTSJ API's to implement these mechanisms and some minor modification suggestions to existing ones as a feed back from our RTSJ experiences. We demonstrates the efficiency of the modified algorithms through extensive simulations and the implementability on available RTSJ compliant virtual machine by an overhead measure in real situation with the RTSJ JamaïcaVM from Aïcas. We also measure the overhead on LejosRT, an RTSJ compliant firmware for Lego Mindstorms NXT in development

The Design and Implementation of Real-time Event-based Applications with RTSJ

International audienceThis paper presents a framework to design real-time event-based applications using Java. The Real-Time Specification for Java (RTSJ) is well designed for hard periodic real-time systems. Though it also proposes classes to model asynchronous events and deal with sporadic or aperiodic tasks, it remains insufficient. The literature proposes the use of periodic servers called task servers to handle nonperiodic traffics in real-time systems. Unfortunately, there is no support for task servers in RTSJ. In order to fix this lack, we propose an RTSJ extension model. To validate our design, we adapt and implement two policies: the polling server and the deferrable server policies. To show how effi- cient these policies are, we compare implementation results and results obtained with a discrete-event-based simulato

RTSJ Extensions: Event Manager and Feasibility Analyzer

International audienceWe present in this paper our experience on the implementation with RTSJ of advanced algorithms to handle aperiodic traffic. We have adapted existing algorithms in order to take into account some constraints brought about by the use of Java language, and our aim which is to propose a portable mechanism. To circumscribe some difficulties, we had to use some programming ruses which could be better integrated into the specification. From these experiences resulted a set of modifications to the specification which we propose to submit to the community in this paper, in addition to a unified event manager framework

Slack-Time Computation for Temporal Robustness in Embedded Systems

International audienceWe propose to handle execution duration overruns (temporal faults) in real-time embedded systems. When a temporal fault occurs, the slack time can be dynamically determined and assigned to the faulty task in order to complete its treatment. This mechanism improves the temporal robustness of real-time systems. We demonstrate that an approximate slack stealer algorithm like the MASS algorithm is a good solution for real-time embedded systems. We validate the feasibility of this approach by an implementation on the Lego Mindstorm NXT platform

Response Time Analysis for Thermal-Aware Real-Time Systems Under Fixed-Priority Scheduling

International audienceThis paper investigates schedulability analysis for thermal-aware real-time systems. Thermal constraints are becoming more and more critical in new generation miniaturized embedded systems, e.g. Medicals implants. As part of this work, we adapt the PFPasap algorithm proposed in [1] for energy-harvesting systems to thermal-aware ones. We prove its optimality for non-concrete1 fixed-priority task sets and propose a response-time analysis based on worst-case response-time upper bounds. We evaluate the efficacy of the proposed bounds via extensive simulation over randomly-generated task systems

Optimal Real-Time Scheduling Algorithm for Fixed-Priority Energy-Harvesting Systems

In a precedent work we saw that finding efficient scheduling algorithms for fixed-priority energy-harvesting systems is one of the challenges of this research area. We presented PFPasap which is an optimal scheduling algorithm. Moreover, the optimality of this algorithm relies on two main assumptions: the considered task sets are energy-non-concrete, and all the tasks consume more energy than it is replenished. Unfortunately, removing one of these two assumptions leads PFPasap to lose its optimality. This is due to the fact that without these assumptions, the worst-case scenario of PFPasap is no longer the synchronous activation with the minimum battery capacity. Moreover, without these assumptions, the worst-case scenario is unknown up to now. There exist some counter examples that prove the non-optimality of PFPasap.The challenge now is to understand why does PFPasap lose its optimality and we try to study deeply the fixed-priority scheduling for energy-harvesting systems by trying to build an optimal algorithm or otherwise to prove the nonexistence of such an algorithm.In this work, we explore different intuitive ideas of scheduling algorithms and we explain why they are not optimal through counter examples. Then, we show the difficulty of finding an optimal algorithm or proving the nonexistence of such an algorithm with a reasonable complexity

Dual Priority and EDF: a closer look

International audienceIn the context of uniprocessor scheduling, two scheduling algorithms have beenvery much studied: one in the class of fixed task priority (FTP) where RateMonotonic (RM) is optimal and one in the class of fixed job priority (FJP),where Earliest Deadline First (EDF) is optimal. RM has the disadvantage ofimposing processor utilization less than 100% (i.e., 69% in the worst case) whileEDF scheduling can reach 100% of processor utilization.Some research have been done to overcome this sub-optimality problem. Ithas been shown that when periods are harmonic, the processor utilization boundof RM is identical to the one of EDF [1]. When no constraint is imposed on theperiods, the dual priority approach was introduced in 1993 [3]. The schedulerconsider two priorities and two phases for each task, each phase has a fixedpriority, the transition from a phase to another is made at a fixed time offsetfrom the task release. Dual priority approach is interesting as it is conjecturedthat a dual priority scheduling can reach the same performances as an EDFscheduler.In this paper, we revisit dual priority scheduling for uniprocessor systemswith implicit-deadline periodic task set. We recall existing conjectures. Then,we explicit a new class of scheduling FPk, a fixed priority scheduling that requiresat most k promotions at k fixed times. We show that dual priority and EDFscheduling are particular cases of FPk. Finally, we analyse EDF scheduling tryingto study how far it is from a dual priority scheduler in terms of promotions

The Optimality of PFPasap Algorithm for Fixed-Priority Energy-Harvesting Real-Time Systems

International audienceThe paper addresses the real-time xed-priority scheduling problem for battery-powered embedded systems whose energy storage unit is replenished by an environmental energy source. In this context, a task may meet its deadline only if its cost of energy can be satis ed early enough. Hence, a scheduling policy for such a system should account for properties of the source of energy, capacity of the energy storage unit and tasks cost of energy. Classical fixed-priority schedulers are no more suitable for this model. Based on these motivations, we propose PFPasap an optimal scheduling algorithm that handles both energy and timing constraints. Furthermore, we state the worst case scenario for non concrete tasksets scheduled with this algorithm and build a necessary and su cient feasibility condition for non concrete tasksets. Moreover, a minimal bound of the storage unit capacity that keeps a taskset schedulable with PFPasap is also proposed. Finally, we validate the proposed theory with large scale simulations and compare our algorithm with other existing ones